计算脚麻由于加入问题

Question

表 -

+----+-----------+-----------+---------+---------------------+------------+ 
| ID | Client_Id | Driver_Id | City_Id |  Status  | Request_at | 
+----+-----------+-----------+---------+---------------------+------------+ 
| 1 |   1 |  10 |  1 | completed   | 2013-10-01 | 
| 2 |   2 |  11 |  1 | cancelled_by_driver | 2013-10-01 | 
| 3 |   3 |  12 |  6 | completed   | 2013-10-01 | 
| 4 |   4 |  13 |  6 | cancelled_by_client | 2013-10-01 | 
| 5 |   1 |  10 |  1 | completed   | 2013-10-02 | 
| 6 |   2 |  11 |  6 | completed   | 2013-10-02 | 
| 7 |   3 |  12 |  6 | completed   | 2013-10-02 | 
| 8 |   2 |  12 |  12 | completed   | 2013-10-03 | 
| 9 |   3 |  10 |  12 | completed   | 2013-10-03 | 
| 10 |   4 |  13 |  12 | cancelled_by_driver | 2013-10-03 | 
+----+-----------+-----------+---------+---------------------+------------+ 

我尝试 -

WITH src 
    AS (SELECT Count(status) AS Denom, 
       request_at 
     FROM trips 
     WHERE status = 'completed' 
     GROUP BY request_at), 
    src2 
    AS (SELECT Count(status) AS Num, 
       request_at 
     FROM trips 
     WHERE status <> 'completed' 
     GROUP BY request_at) 
SELECT Cast(Count(num) AS FLOAT)/Cast(Count(Denom) AS FLOAT) AS cancel_rate, 
     trips.request_at 
FROM src, 
     src2, 
     trips 
GROUP BY trips.request_at; 

我试图找到每天的取消率，但它正在清除错误（ MY OUTPUT） -

+-------------+------------+ 
| cancel_rate | request_at | 
+-------------+------------+ 
|   24 | 2013-10-01 | 
|   18 | 2013-10-02 | 
|   18 | 2013-10-03 | 
+-------------+------------+ 

2013-10-01的取消费率应为0.5而非24.与其他日期类似，它应该不同。

我知道问题出在这一部分，但我不知道什么是正确的方法或如何处理它

SELECT Cast(Count(num) AS FLOAT)/Cast(Count(Denom) AS FLOAT) AS cancel_rate, 
     trips.request_at 
FROM src, 
     src2, 
     trips 

有没有什么办法可以把超过1个select语句中With NAME as()条款？这样我就不会使用任何JOIN或多个表。

Answer 1

使用条件汇总：

SELECT SUM(CASE WHEN status = 'completed' THEN 1 ELSE 0 END) as denom, 
     SUM(CASE WHEN status <> 'completed' THEN 1 ELSE 0 END) as num, 
     AVG(CASE WHEN status <> 'completed' THEN 1.0 ELSE 0 END) as cancel_rate 
FROM trips 
GROUP BY request_at; 

注意计算为cancel_rate。使用AVG()而不是将这两个值分开比较简单。使用1.0是因为SQL Server执行整数运算，所以1/2是0而不是0.5。

Answer 2

OK，有些又迟到，但这里是另一种变体（编辑）：

SELECT SUM(CASE LEFT(status,9) WHEN 'cancelled' THEN 1. ELSE 0 END) 
     /COUNT(*) cancellation_rate, 
     request_at 
FROM trips GROUP BY request_at ORDER BY request_at